Multiwavelength Photoacoustic Measurements of Light Absorption and Scattering by Wood Smoke

More Specific Title:Evidence for light absorption by organic carbon species

in woodsmoke.

Kristin Lewis, William P. Arnott, and Stephanie WinterUniversity of Nevada Reno Physics Department

Hans Moosmuller and the Desert Research Institute

Reno Nevada USA

Claudio Mazzoleni Los Alamos National Laboratory

Los Alamos NM USA

People and Instruments

Missoula Wood Smoke Optics and Chemistry Experiment

• Photoacoustic instruments at1047 nm870 nm780 nm532 nm405 nm

• 7 wavelength Aethalometer• Aerodyne Mass Spec• TDMA, CCN, SEM, CRD, Mercury, NO2, Ozone, TSI 3

lamba Neph, Radiance Nephs, Scattering hygroscopicity, TEOM, EC/OC, and more…

• Optical, chemical, and microphysical properties of varied wood smoke aerosols were measured at the Missoula Fire Sciences Laboratory June 2006.

• For each of the 16 fuel types, 200 grams of fuel were ignited. The smoke was contained in a burn chamber and sampled for two hours.

Sample InletSample Outlet

Input

Coupler

Output

Coupler

Piezoelectric

Transducer

Microphone and

Surrounds

RESONATOR

SECTION

COUPLING

SECTION

COUPLING

SECTION

Photodetector

C osine-

Weighted

Sensor.

Scattering

Measurement.

Fiber-coupled

to PMT.

LASER 1

LASER 2

LASER 3

Fiber 1

Fiber 3

Fiber 2

Culmination

Fiber

405nm

870 nm

Photoacoustic Instrument Schematic: First Measurements with a Multi-Wavelength Photoacoustic Instrument for Aerosol Light

Scattering And Absorption

Angström Coefficients and Single Scattering Albedo

Bsca = aλ−b

Babs = cλ−d

ϖ =Bsca

Bext

=Bsca

Bsca + Babs

Measurements at 2 wavelengths are used to obtain a, b, c, and d Angström coefficients for absorption and scattering.

The typical assumption for absorption is d = 1 for elemental carbon.

Single scattering albedo is obtained at each wavelength.

• For certain fuel types burned aerosol light absorption did not display the 1/λ dependence on incident wavelength that is characteristic of small elemental carbon aerosol.

• Absorption can be far more efficient at the near-UV wavelength than in the near-infrared.

Absorption by Wood Smoke

0

10000

20000

30000

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60000

17:0217:0817:1417:2017:2817:3417:4017:4617:5418:0018:0618:1218:2018:2618:3218:3818:4618:5218:58Time

Aethalometer Black Carbon (ng m

-3)

0

100

200

300

400

500

600

Photoacoustic B

abs

(Mm

-

UV - 370 nmBlue - 470 nmIR - 880 nm405nm Absorption (Photoacoustic)870nm Absorption (Photoacoustic)

Chamise: Single Scattering Albedo = 0.40 at 405 nm

PA Absorption Angstrom Coef. = 1.18

0

5000

10000

15000

20000

25000

30000

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50000

8:328:388:448:508:589:049:109:169:229:309:369:429:489:54Time

Aethalometer Black Carbon (ng m

-

0

50

100

150

200

250

300

Photoacoustic B

abs

(Mm

-

UV - 370 nm

Blue - 470 nm

IR - 880 nm

405 nm (Photoacoustic)

870 nm (Photoacoustic)

Rice Straw Fuel: Single Scatter Albedo = 0.88 at 405 nm

Aeth 370 nm

Aeth 470 nm

Aeth 880 nm

PA 405 nm

PA 880 nm

Absorption Angstrom Coef

= 2.81

Angstrom Coefficient for Absorbtion vs. Single Scattering Albedo at 405 nm

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Single Scattering Albedo, 405 nm

Angstrom Coefficient of

Absorbtion

Ponderosa Pine,mixed fuelsChamise

Ponderosa Pine,mixed fuelsChamise

Rice Straw

Ponderosa Pine Duff

Alaskan Duff

So. CalifornianManzanitaSage & Rabbitbrush

Lignin

Lodgepole Pine,mixed fuelsUtah Juniper,foilage/twigsPuerto Rico Fern

Chamise

Wax Myrtle,branches/foilageSouthern Pine,needlesPuerto Rico, mixedwoodsPalmetto

Ceanothus

Brushes and Shrubs.

Pine, evergreen, palm mixed woods: needle litter, branches, and foilage.

Duff, ferns, and rice straw.

Angstrom Coefficient for Absorbtion vs.Single Scattering Albedo at 532 nm

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

0.2 0.4 0.6 0.8 1Single Scattering Albedo, 532 nm

Angstrom Coefficient of Absorbtion(from Babs at 532 & 870 nm)

Ponderosa Pine,mixed fuelsChamise

Ponderosa Pine,mixed fuelsChamise

Rice Straw

Ponderosa Pine Duff

Alaskan Duff

So. CalifornianManzanitaSage & Rabbitbrush

Lignin

Lodgepole Pine,mixed fuelsUtah Juniper,foilage/twigsPuerto Rico Fern

Chamise

Wax Myrtle,branches/foilageSouthern Pine,needlesPuerto Rico, mixedwoodsPalmetto

Ceanothus

Brushes and Shrubs.

Pine, evergreen, palm mixed woods: needle litter, branches, and foilage.

Duff, ferns, and rice straw.

Conclusion• Non-elemental-carbon components, such as organic

species, exist on smoke aerosol of certain fuel types and preferentially absorb light at shorter wavelengths. In addition to particle size, differences in refractive index at widely differing wavelengths contribute to spectral properties of the aerosol.

• Casual use of the inverse wavelength dependence of aerosol light absorption in remote sensing retrievals with sun photometers and satellite data can bring errors of a factor of 6 in the UV and a factor of 2 in the visible when compared with near IR absorption for certain types of wood smoke.

ACKNOWLEDGEMENTS:DOE ASP Program and the National Parks Service, field work.NSF MRI program for instrument development.All participants in the Missoula Fire Experiment.